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Copyright: 2011. The Objects Group Wiki pages are a publication of the Objects Specialty Group of the American Institute for Conservation of Historic and Artistic Works. The Objects Group Wiki pages are published for the members of the Objects Specialty Group. Publication does not endorse or recommend any treatments, methods, or techniques described herein.
Skeletal materials are organics primarily composed of varying percentages of hydroxyapatite and collagen, and can take the form of bone, antler, ivory, teeth, or horn. To first identify whether a material is skeletal, one must look for a porous surface, or unique shape. With X-ray or ultraviolet light, or even low magnification, the examination of a cross-section or broken fragment can identify indicative soft, spongy features (versus striated), delamination, surface pores, and flakiness, depending on the object’s deterioration (SHA 2007).
Skeletal materials can be strong and well preserved when dry, especially if maintained in a fixed relative humidity (RH) (Cronyn 1990:279), optimally maintained at a long-term 50%-60% (Kuhn 1986:118). Thus, some basics for conserving bone focus on stabilizing the artifact with appropriate long-term RH (Cronyn 1990:274). This means that, like all organics, shocking the artifact by introducing extreme RH changes must be avoided, as it can result in cracking and warping (CCI 1988:2). Generally, one should not allow dry materials to get wet, and should prevent fluctuations of ambient RH when an artifact is in storage or on display.
Treatment of Archaeological Bone
If the object is in a stable state, it must be examined minutely for damage, and then very carefully cleaned. For dry and sturdy bone, delicately cleansing with a 1:1 ethanol/water solution is advised (SHA 2007). This must be done with the greatest caution, as the porous nature of skeletal materials means that they can stain easily, and the composition of these objects prevents most chemical cleaning ([[#ref1|Cronyn 1990]). Additionally, the delicate surface of a skeletal object can be easily marked, which means a great deal of expertise and precision is required to clean skeletal materials. Kuhn recommends for dry stable skeletal materials, “Ivory and bone carvings that are not in a fragile or brittle state may be cleaned with a soft brush and water to which a little alcohol and a small amount of a mild detergent has been added. Because of the hygroscopic nature of the material, ivory and bone objects should be evenly moistened from all sides, as near simultaneously as possible” (Kuhn 1986).
Once the bone has been cleaned, it is frequently treated with a consolidant to impart structural strength. A common application is a 5-10% solution of Acryloid B-72 in an acetone solvent. “Vacuum impregnation of the B-72 solution is often employed in order to ensure maximum penetration” (SHA 2007). Though the consolidant procedure will impart strength, it is also important to note that consolidant applications can be irreversible, and prevent future analysis of the artifact. In summary, it is critical to maintain skeletal materials at a stable RH and prevent them from getting wet. Cleaning is a laboratory process that is primarily mechanical, and must be done with the utmost care; usually stains cannot be removed. Consolidants can be applied to aid structural integrity, but can have long-term impact on potential future artifact analysis.
Canadian Conservation Institute. 1988. CCI Notes 6/1 Care of Ivory, Bone, Horn, and Antler. In: CCI Notes, pp. 1-4.
Cronyn, J. 1990. Chapter 6.4 Skeletal Material. In: The Elements of Archaeological Conservation, pp. 275-282.
Jenssen, V. 1987. Section 8.9 and 8.11, Conservation of Wet Organic Artefacts Excluding Wood. In: Conservation of Marine Archaeological Objects, pp. 156-162.
Kuhn, H. 1986. Chapter 9: Ivory and Bone. In: Conservation and Restoration of Works of Art and Antiquities-Volume 1, pp. 116-119.
SHA. 2007. FAQs Treatment of Bone, . Accessed 3/25/13.